Topic 6 - Radioactivity

Question 1

Describe an atom

Answer 1

A positively charged nucleus, consisting of protons and neutrons, surrounded by negatively charged electrons, with the nuclear radius much smaller than that of the atom and with almost all of the mass in the nucleus

Question 2

What is the typical order of magnitude of an atom?

Answer 2

10⎺¹⁰m

Question 3

What is the typical order of magnitude of a small molecule?

Answer 3

10⎺⁹m (1nm)

Question 4

How is the structure of nuclei of isotopes represented?

Answer 4

By a mass (nucleon) number to the top left and an atomic (proton) number to the bottom left of the symbol of a element

Question 5

Describe the charge of the nucleus of every element

Answer 5

The nucleus of each element has a characteristic positive charge

Question 6

How do isotopes differ?

Answer 6

Isotopes of an element differ in mass by having different numbers of neutrons

Question 7

State the relative masses of protons, neutrons, electrons and positrons

Answer 7

Proton = 1
Neutron = 1
Electron = 1/1835
Positron = 1/1835

Question 8

State the relative charges of protons, neutrons, electrons and positrons

Answer 8

Proton = +1
Neutron = 0
Electron = -1
Positron = +1

Question 9

Describe the relationship between protons and electrons

Answer 9

In an atom the number of protons equals the number of electrons and the charge is therefore neutral

Question 10

How do electrons interact with their nucleus?

Answer 10

In each atom its electrons orbit the nucleus at different set distances from the nucleus

Question 11

Explain what happens when there is absorption of electromagnetic radiation

Answer 11

When there is absorption of electromagnetic radiation/energy electrons move to a higher orbit.
The more the energy the greater the orbit move until the electron has absorbed enough energy to escape from the atom. The atom no longer has enough electrons to balance all the positive charges on the protons: so then becomes a positive ion.

Question 12

Explain what happens when there is emission of electromagnetic radiation

Answer 12

When energy/electromagnetic radiation is emitted from an electron it moves to a lower orbit.

Question 13

What causes the emission of alpha, beta minus, positron, gamma rays and neutron radiation?

Answer 13

They are emitted from unstable nuclei in a random process

Question 14

What type of radiation is alpha, beta minus and positron?

Answer 14

Ionising radiation

Question 15

Explain what is meant by background radiation

Answer 15

Background radiation is radiation that occurs naturally and is therefore always around us.

Question 16

Describe the origins of background radiation and give examples

Answer 16

Background radiation has natural sources exemplified by space such as living things, rocks food, nuclear and medical sources. Radon is the largest source of it.

Examples:
-Cosmic rays
-Sun
-Rocks
-Buildings
-Food
-Water
-X-rays

Question 17

Describe photographic film as a method of measuring and detecting radioactivity

Answer 17

The photographic film is chemically changed by the radiations —becoming increasingly darker. It can be developed to see if there has been exposure.

Question 18

Describe Geiger-Müller tubes as a method of measuring and detecting radioactivity

Answer 18

In a G-M tube, the radiations ionise the gas inside and the resulting charged particles move across the chamber and get counted as charges rather like an ammeter.

To use a Geiger-Müller tube, place a radioactive source in front of it. Measure the count rate of the source. Keep the source-detector distance the same for each object checked. (Repeat readings, take averages, measure background count for proper experiment)

Question 19

What is an alpha particle equivalent to?

Answer 19

A helium nucleus

Question 20

What is a beta particle equivalent to?

Answer 20

A beta particle is an electron emitted from the nucleus

Question 21

What is a gamma ray equivalent to?

Answer 21

A gamma ray is electromagnetic radiation

Question 22

Describe alpha particles ability to penetrate

Answer 22

Alpha particles are weakly penetrating, only able to pass through skin and paper, and have a range of around 5-6 centimetres in air.

Question 23

Describe beta particles ability to penetrate

Answer 23

Beta particles are medium penetrating, capable of passing through 3mm aluminium foil and it has a range of around 1 metre in air.

Question 24

Describe gamma rays ability to penetrate

Answer 24

Gamma rays are highly penetrating, capable of passing through lead or concrete, and it has a range of over 1 kilometre in air.

Question 25

Compare alpha, beta and gamma particles abilities to ionise

Answer 25

Alpha's ionising power is high, beta's ionising power is moderate and gamma rays are weakly ionising.

Question 26

Describe Dalton's model

Answer 26

1800s - suggested atoms are solid spheres

Question 27

Describe Thompson's Plum Pudding model

Answer 27

1904 - Suggested an atom is largely positively charged mass with negatively charged particles scattered throughout. This was the first suggestion that atoms contained parts with negative and positive charges.

Question 28

Describe Rutherford's alpha particle scattering experiment

Answer 28

1905 - Ernst Rutherford carried out the gold foil experiment where he fired alpha particles at gold foil. Based on the plum pudding model all the particles should've passed straight through. However, while some particles did go straight through, many deflected at angles. This indicated that there was a central nucleus where mass was concentrated and particles which deflected at large angles directly hit the nucleus and those that deflected at small angles hit the edge of the nucleus. This led to Rutherford's model showcasing that the atom is mainly empty where positive charge is concentrated, surrounded by negatively charged particles.

Question 29

Describe Bohr's model

Answer 29

1913 - Bohr revised Rutherford's model by suggesting electrons orbited the nucleus in different energy levels. By doing this, he was able to explain that different elements burn with different coloured flames because their electrons have different energy levels. It also explains emission and absorption in relation to electrons.

Question 30

Describe the process of β– decay

Answer 30

If the nucleus has too many neutrons, a neutron will turn into a proton and electron. This electron is called a beta particle. The atomic number increases by 1 but there is no change to the mass number.

Question 31

Describe the process of β+/positron decay

Answer 31

If the nucleus has too few neutrons, a proton will turn into a neutron and emit a fast moving positron which can be called a β+ particle. The atomic number goes down by 1 but the mass number does not change

Question 32

Explain alpha decay

Answer 32

If the nucleus is unstably large it will emit 2 protons and 2 neutrons called an alpha particle. This alpha particle is also a Helium-4 nucleus (⁴₂He or ⁴₂α). Alpha decay causes the atomic number of the nucleus to decrease by 2 and the mass number of the nucleus to decrease by 4.

Question 33

Explain gamma decay

Answer 33

In gamma decay the nucleus is rearranged to make it more stable - this may cause the nuclei to lose energy as gamma radiation. Undergoing gamma decay does not change the structure of composition of the atom as gamma rays carries no charge and doesn't have an associated mass.

Question 34

Explain the effects of neutron emission

Answer 34

Neutron emission can be caused by a variety of methods, such as the absorption of cosmic rays or nuclear fission. In neutron emission a neutron is ejected from a nucleus. The atomic number does not change but the mass number goes down by 1.

Question 35

Describe the relationship between radioactive decay and gamma radiation

Answer 35

Nuclei that have undergone radioactive decay often undergo nuclear rearrangement with a loss of energy as gamma radiation

Question 36

Describe how the activity of a radioactive source decreases over a period of time

Answer 36

Activity is the number of decays in a sample per second. Activity is initially very high because, as decay is random, the more atoms in the sample, the greater the chance at least one of them will decay. This will decrease exponentially over time.

Question 37

What is the unit of activity of a radioactive isotope?

Answer 37

Becquerel (Bq)

Question 38

Explain what the half-life of a radioactive isotope is

Answer 38

The time taken for half the undecayed nuclei to decay // The time taken for the activity of a source to decay by half

Question 39

Why is half-life useful?

Answer 39

It cannot be predicted when a particular nucleus will decay but half-life enables the activity of a very large number of nuclei to be predicted during the decay process

Question 40

How would you draw a graph representing how a radioactive sample is decaying over time?

Answer 40

Activity (becquerels) on y-axis and time (days/etc.) on the x-axis. The curve should be decreasing downwards to the right but never touch the bottom of the x-axis

Question 41

Describe the use of radioactivity in household fire (smoke) alarms

Answer 41

Alpha particles ionise air particles and make them charged, therefore making a current. A household smoke alarm measures the movement of alpha particles across a small gap. If smoke enters the detector, it will absorb the alphas (as alpha particles are easily absorbed) and the detector will measure a drop in the number getting across the gap. This drop in measurement will trigger the alarm to sound.

Question 42

Describe the use of radioactivity in irradiating food

Answer 42

Gamma rays transfer energy to bacteria, killing them. This sterilises the food to make it safer to eat and so it can be stored for longer before going off.

Question 43

Describe the use of radioactivity in the sterilisation of equipment

Answer 43

Radiation, usually gamma rays, exposed onto equipment kill all microbes present - sterilising the equipment through irradiation

Question 44

Describe the use of radioactivity in tracing and gauging thickness

Answer 44

A source and receiver are placed either side of the paper during its production. The thickness of a material can be gauged by measuring the amount of radiation that passes through (isn't absorbed). This is often used with a beta particle detector to test the thickness of paper. The thinner the paper, the higher count rate that is detected.

Question 45

Describe the use of radioactivity in the diagnosis and treatment of cancer

Answer 45

-A gamma emitter can be used as a tracer. After being consumed or injected, it passes through the body and an external detector pictures where the tracer has collected in the body to reveal tumours. -Gamma rays can also be used on a tumor to kill the cancer cells.

Question 46

Describe the dangers of ionising radiation

Answer 46

Large amounts of ionising radiation can cause radiation burns and sickness or it can impair the function of tissues. Smaller amounts can alter chemicals reactions and kill cells. Over long periods this could cause mutations in DNA which could lead to cancer.

Question 47

Explain how the dangers of ionising radiation depend on half life

Answer 47

A source with a long half-life's damaging effect will last longer. A source with a short half-life is initially very radioactive but does not remain so and its radioactivity decreases quicker than the one with a short half-lifes'. Sources with short half-life's are a better option for medical application as they pose less of a long-term risk.

Question 48

Explain the precautions taken to ensure the safety of people exposed to radiation (Describe 3 precautions)

Answer 48

-Keep distance from the source -Handle the source with tongs -Wear a dosimeter badge to detect the amount of radiation you are exposed to -Use shielding -Limit exposure time -Wear protective clothing to prevent the body from being contaminated -Keep radioactive sources in a lead-lined box when not in use

Question 49

Describe contamination

Answer 49

It is caused by touch, injestion or injection of radioactive materials. It lasts for a long period of time, as long as the source is on or in it. The source of the radiation is transferred to an object. Once an object is contaminated, the radiation cannot be blocked. It can be very difficult to remove all of the contamination.

Question 50

Describe irradiation

Answer 50

It is caused by exposure to a source of radiation which reaches an object. Lasts only for a short period of time. It doesn't cause the object to become radioactive. It can be blocked with suitable shielding. It stops as soon as the radioactive source is removed.

Question 51

Compare the hazards of contamination and irradiation

Answer 51

-Radioactive contaminants emit ionising radiation, which can penetrate and damage living tissues. Exposure to radioactive contaminants can lead to various health issues, including cancer, genetic mutations, and radiation sickness. -The hazards of irradiation primarily depend on the dose and duration of exposure to ionising radiation. High doses of radiation can cause acute radiation sickness, while long-term exposure to low doses may increase the risk of cancer.

Question 52

Evaluate the treatment of tumours using radiation applied externally

Answer 52

A beam of gamma radiation rotates around the body. It continually focuses on the tumour, while only passing momentarily across heathy cells surrounding the tumour. Advantage: -This ensures minimal damage against healthy cells and many affecting the tumour. Disadvantages: -It takes a long time to fully treat the tumour, taking multiple visits and around 5 weeks. -There is a greater risk of long-term side effects, as the radiation passes through healthy tissues.

Question 53

Describe the treatment of tumours using radiation applied internally

Answer 53

Radioactive material is held within a needle and injected directly into the tumour. Disadvantage: -A longer period of time needs to be spent in hospital, as some radioactive implants are of high radioactivity so you emit radiation, requiring you to have limited contact with visitors until the source's activity has decreased.

Question 54

Explain the use of radioactive substances in PET scanners in the diagnosis of medical conditions

Answer 54

In Positron Emission Tomography a radioactive tracer is inserted into the body and tagged to the desired chemical. The tracer therefore travels in the body where this chemical travels. The scanner records where the tracer emits radiation. This produces a live 3D visualisation of the body. It is used to show how effective current treatment is or to diagnose cancer, epilepsy or Alzheimer's

Question 55

Explain why isotopes used in PET scanners have to be produced nearby

Answer 55

This because the tracer usually has a short half-life so cannot be stored for long before it decays; it must therefore be used as soon as possible after making.

Question 56

What are the advantages of nuclear power? (Name 3)

Answer 56

-No carbon dioxide emissions -More energy per kg This also reduces mining and transportation effects on the environment -No cross-country pipelines -Does not contribute to global warming -Produces no polluting gases -High technology research required benefits other industries. -Power station has very long lifetime.

Question 57

What are the disadvantages of nuclear power? (Name 3)

Answer 57

-Public perception that radioactivity is dangerous -There is a safety risk of radiation leaking from plants -Risk of terrorist attacks to try and obtain radioactive material -Large-scale nuclear accidents can be catastrophic -Nuclear waste is radioactive for a long time -Disposal is difficult and expensive

Question 58

How can you gain energy from nuclear sources?

Answer 58

Nuclear reactions, including fission, fusion and radioactive decay, can be a source of energy

Question 59

Explain the nuclear fission of U-235

Answer 59

A neutron is absorbed by a U-235 nucleus which makes it unstable so it splits. The produces two daughter nuclei and the emission of two or more neutrons, accompanied by a release of energy. 1 or more of the released neutrons are absorbed by other nuclei. They cause further fission reaction reacts. These further fission reactions release further neutrons which result in a chain reaction as they trigger other cases of nuclear fission.

Question 60

Why does a nuclear chain reaction need to be controlled?

Answer 60

A chain reaction needs to be controlled as more neutrons are released than the number absorbed which could cause an exponential process. it could cause a meltdown.

Question 61

Explain how the chain reaction is controlled in a nuclear reactor

Answer 61

Neutrons are released in a chain reaction. Slower neutrons are needed for fission. Some neutrons are too fast. Control rods can be moved in and out to control the speed of the reaction. These rods absorb neutrons to stop them travelling between fuel rods and make more or fewer neutrons available for fission to change the speed of the chain reaction. A moderator (usually water or a graphite core) slows down the neutrons so that they are more likely to be absorbed into a nearby fuel rod.

Question 62

Describe how thermal (heat) energy from the chain reaction is used in the generation of electricity in a nuclear power station

Answer 62

The heat energy from the chain reaction is absorbed by the coolant (water) which is heated up by the energy released from fission reactions and boils the water to produce steam that turns a turbine, which turns the generator that generates electricity.

Question 63

Describe the main feature of the products of nuclear fission

Answer 63

The products of nuclear fission are radioactive

Question 64

Describe nuclear fusion

Answer 64

The creation of larger nuclei from smaller nuclei joining, this results in a loss of mass from smaller nuclei, accompanied by a release of energy and helium.

Question 65

What is fusion the energy source for?

Answer 65

Stars

Question 66

State the advantages and disadvantages of nuclear fission

Answer 66

Advantages: -Already in use Disadvantages: -Waste is radioactive -Waste is hard to dispose of -Risk of accident

Question 67

State the advantages and disadvantages of nuclear fusion

Answer 67

Advantages: -No harmful waste products Disadvantages: -Not achieved yet on a practicable scale -Difficulty in achieving high energy/temperature/pressure/paricle density

Question 68

Describe the requirements for nuclear fusion and why

Answer 68

High temperatures and pressure are required to overcome electrostatic repulsion of protons between nuclei.

Question 69

What are the conditions for fusion that make making a practical and economic form of power station difficult?

Answer 69

-The problem of containment (the fusion gases/isotopes at high temperatures) -Maintaining high temperature -Maintaining high pressure